You can make a motto with just one adverb. Normally an adverb modifies a verb, but when the adverbs are used on their own like this, you can imagine a generic sense of doing that goes with them - "(I do things) Bravely," or "(I always act) Cautiously," etc.
Candide - Openly.
Impavide - Fearlessly.
Aequanimiter - Calmly.
Audaciter - Boldly.
Fideliter - Faithfully.
Fortiter - Bravely.
Mediocriter - Moderately.
Suaviter - Pleasantly.
Constanter - Steadfastly.
Patienter - Patiently.
Vigilanter - Wathcfully.
Paulatim - Gradually.
Subito - Immediately.
Sursum - Upward.
It is possible to combine two or three adverbs simply with a comma:
Candide, sincere - Openly, with integrity.
Honeste, fortiter - Honorably, bravely.
Suaviter, fortiter - Pleasantly, bravely.
Cito, tuto, iucunde - Swiftly, safely, gladly.
Citius, altius, fortius - More swiftly, higher, more strongly.
Fortiter, fideliter, feliciter - Bravely, faithfully, happily.
Pulchre, bene, recte - Nicely, rightly, properly.
Scite, citissime, certe - Ingeniously, mostly swiftly, surely.
Sagaciter, fideliter, constanter - Keenly, faithfully, steadfastly.
You can easily combine two adverbs with the word et:
Nunc et semper - Now and always.
Semel et semper - Once and for always.
Aequabiliter et diligenter - Fairly and carefully.
Aequaliter et diligenter - Evenly and carefully.
Audacter et aperte - Boldly and openly.
Audacter et sincere - Boldly and with integrity.
Callide et honeste - Wisely and honorably.
Candide et caute - Openly and cautiously.
Candide et constanter - Openly and steadfastly.
Candide et secure - Openly and without worry.
Caute et sedulo - Cautiously and carefully.
Celeriter et iucunde - Swiftly and gladly.
Consulto et audacter - Purposefully and boldly.
Copiose et opportune - Eloquently and appropriately.
Fideliter et diligenter - Faithfully and carefully.
Fideliter et recte - Faithfully and properly.
Fortiter et celeriter - Bravely and swiftly.
Fortiter et feliciter - Bravely and happily.
Fortiter et fideliter - Bravely and faithfully.
Fortiter et recte - Bravely and properly.
Fortiter et strenue - Bravely and energetically.
Recte et suaviter - Properly and pleasantly.
Sapienter et pie - Wisely and piously.
Sincere et constanter - Sincerely and steadfastly.
Strenue et audacter - Energetically and boldly.
Strenue et prospere - Energetically and successfully.
Suaviter et fortiter - Pleasantly and bravely.
Tuto et celeriter - Safely and swiftly.
Tuto, celeriter, et iucunde - Safely, swiftly, and gladly.
The enclitic -que can serve the same purpose:
Cito fideliterque - Swiftly and faithfully.
Iterum, iterum, iterumque - Again, again, and again.
The conjunction ac can also join two adverbs:
Fortiter ac sapienter - Bravely and wisely.
The conjunction "or" may also be used:
Nunc aut nunquam - Now or never.
You can also set off contrasting adverbs with sed as the conjunction:
Candide, sed caute - Openly, but cautiously.
Comiter, sed fortiter - Courteously, but bravely.
Fortiter, sed apte - Bravely, but suitably.
Lente, sed attente - Slowly, but conscientiously.
Lente, sed opportune - Slowly, but suitably.
Paulatim, sed firmiter - Gradually, but firmly.
Sero, sed serie - Late, but earnestly.
Suaviter, sed fortiter - Pleasantly, but boldly.
You can also make a motto by negating an adverb:
Non frustra - Not in vain.
Non temere - Not rashly.
Non temere, sed fortiter - Not rashly, but boldly.
Cito, non temere - Swiftly, not rashly.
Caute, non astute - Cautiously, not cunningly.
Caute, nec timide - Cautiously, and not timidly.
You can also negate two adverbs as neither-nor:
Nec cito, nec tarde - Neither swiftly, nor late.
Nec temere, nec timide - Neither rashly, nor fearfully.
Nec timide, nec temere - Neither fearfully, nor rashly.
Neque profuse neque avare - Neither lavishly nor stingily.
You can also use one adverb to modify another:
Semper sic - Always thus.
Semper sursum - Always upwards.
Nunquam deorsum - Never downwards.
Nec minus fortiter - No less boldly.
Potius sero quam numquam - Rather late than never.
Nunc, ut olim - Now, as formerly.
You can modify adverbs with conditional statements build using si or nisi:
Sapienter, si sincere - Wisely, if sincerely,
Nisi Dominus frustra - Unless (there is) God, fruitlessly.
Nunquam nisi honorificentissime - Never, unless most honorably.
Prepositional phrases can also be used to modify an adverb:
Sub pondere sursum - Beneath my load, (I look) upwards.
Suaviter in modo, fortiter in re - Sweetly in manner, boldly in action.